Insight into the haem d 1 biosynthesis pathway in heliobacteria through bioinformatics analysis

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Abstract
Haem d 1 is a unique tetrapyrrole molecule that serves as a prosthetic group of cytochrome cd 1, which reduces nitrite to nitric oxide during the process of denitrification. Very little information is available regarding the biosynthesis of haem d 1. The extreme difficulty in studying the haem d 1 biosynthetic pathway can be partly attributed to the lack of a theoretical basis for experimental investigation. We report here a gene cluster encoding enzymes involved in the biosynthesis of haem d 1 in two heliobacterial species, Heliobacillus mobilis and Heliophilum fasciatum. The gene organization of the cluster is conserved between the two species, and contains a complete set of genes that lead to the biosynthesis of uroporphyrinogen III and genes thought to be involved in the late steps of haem d 1 biosynthesis. Detailed bioinformatics analysis of some of the proteins encoded in the gene cluster revealed important clues to the precise biochemical roles of the proteins in the biosynthesis of haem d 1, as well as the membrane transport and insertion of haem d 1 into an apocytochrome during the maturation of cytochrome cd 1.